Active Storage as Attachment in Rails API with base64 decoding

_document.json.jbuilder

json.extract! document, :id, :documentable_type, :documentable_id, :created_at
json.url rails_blob_url(document.doc)

document.rb

class Document < ApplicationRecord
  has_one_attached :doc
  belongs_to :documentable, polymorphic: true, optional: true
  attr_accessor :doc_contents
  attr_accessor :doc_name

  after_create :parse_doc
  validate :doc_validations, on: :create


  def parse_doc
    # If directly uploaded
    unless self.doc_contents.nil? || self.doc_contents[/(image\/[a-z]{3,4})|(application\/[a-z]{3,4})/] == ''
      content_type = self.doc_contents[/(image\/[a-z]{3,4})|(application\/[a-z]{3,4})/]
      content_type = content_type[/\b(?!.*\/).*/]
      contents = self.doc_contents.sub /data:((image|application)\/.{3,}),/, ''
      decoded_data = Base64.decode64(contents)
      filename = self.doc_name || 'doc_' + Time.zone.now.to_s + '.' + content_type
      File.open("#{Rails.root}/tmp/images/#{filename}", 'wb') do |f|
        f.write(decoded_data)
      end
      self.doc.attach(io: File.open("#{Rails.root}/tmp/images/#{filename}"), filename: filename)
      FileUtils.rm("#{Rails.root}/tmp/images/#{filename}")
    end
  end

  private

  def doc_validations
    if self.doc_contents.nil?
      errors.add(:base, I18n.t('errors.documents.file_required'))
    end
  end
end

document_controller.rb

class DocumentsController < ApplicationController
  before_action :authenticate_user, only: %i[create]

  def create
    @document = Document.new(document_params)
    if @document.save
      return success_document_save
    else
      return error_save @document
    end
  end

  protected

  def success_document_save
    render status: :created, template: 'documents/show.json.jbuilder'
  end

  def error_save obj
    render status: :unprocessable_entity, json: {errors: obj.errors.full_messages}
  end

  private

  def document_params
    params.permit(:doc_contents, :doc_name)
  end
end

documentmigration.rb

class CreateDocuments < ActiveRecord::Migration[5.2]
  def change
    create_table :documents do |t|
      t.references :documentable, polymorphic: true, index: true

      t.timestamps
    end
  end
end

en.yml

en:
  errors:
    documents:
      file_required: "file attachment is required"
      content_type: "attachment must be image or pdfs"

show.json.jbuilder

json.partial! 'documents/document.json.jbuilder', document: @document